Keep in mind that only the latest version of the game is officially supported and players reverting to a previous version are doing so at their own responsibility. Should you encounter any issues on an older version of the game make sure to update it first.
However, if for any reason you wish to revert to an earlier version of the game, here's how you can do it:
1. Go to your Steam Library.
2. Right-click on The Witcher 3: Wild Hunt and select Properties.
3. Go to BETAS and select CLASSIC - the game will update automatically.
To return to the newest version of the game, simply follow the same steps and select "None" in the BETAS menu.
1. Go to your “Installed” section on GOG Galaxy
2. Select The Witcher 3: Wild Hunt and select Manage Installation → Configure…
3. Disable the auto-updates option, choose your preferred version, and click OK.